Last Update: 03.05.2020
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Objective
On this page we are going to
- install the motor bulkhead and the motor
- assemble motor and spinner
- decide upon the airscrew and voltage configuration
- assemble and install the airscrew
- prepare the wiring harness to connect the controller to the motor and to the battery and program the controller
- give it a test run
1. Bulkhead & Motor
The Roxxy motor set contains a lot of alternative parts. We only need the motor, four countersunk bolts for the bulkhead and the three connectors with the coloured shrink-on tubes for the controller.
We are using the bulkhead which came with the Taser kit. Its bolt circle does not completely match the mixed 16/19mm bores of the motor. We have to enlarge and countersink the holes anyway. So correction is applied by doing this 1.5mm off-centre for 2 of them.
This is what we are aiming for: The bulkhead is not completely flush with the front edge of the fuselage but set back a tiny little bit (approx. 0.2 to 0.3mm). This will leave some room for glue without spoiling PCM’s tidy work on the front edge of the fuselage. The bulkhead may still look circular but we made it in fact a very rounded hexagon. Its corners will sit on the inner surfaces of the fuselage to define the position of the bulkhead precisely. The sides of the „hexagon“ form hairline gaps between the fuselage and the bulkhead for the epoxy to flow in.
Preparation work on the bulkhead is completed when
- it can be inserted into the fuselage to the selected position without too much force.
- the conical shape of the fuselage keeps it from falling out through the front hole.
- the cross section of the fuselage remains as circular as before and the driveshaft is centred. This is tested with the motor and spinner temporarily in place.
When done, we secure the bulkhead’s position with a drop of superglue. Then it is cast in with UHU plus endfest 300 from inside the fuselage. We apply the glue with a toothpick, drop by drop, through the cockpit opening. Leave it to set for 24 hours hanging nose down. Check once in a while to make sure that
The glossy seam on the right hand side is epoxy which seeped through from the inside as expected while it was curing.
2. Spinner
The spinner is simply plugged on the driveshaft and secured with two headless screws (grub screws). To avoid an unreliable pure force fit, the shaft is flattened by about 0.5mm on one side to make a proper seating for the screw. This will not only help transmitting torque. It also prevents the separation of the airscrew from the shaft in case of unfastened screws. In our setup, the front edge of the recess is 6mm in front of the motor bulkhead.
The shapes of the spinner and the fuselage align perfectly.
3. Airscrew & Voltage Variants
Given the Roxxy motor and controller we already have and an estimated flight weight of 600 grams, there is a multitude of possible configurations for the prop from 7 up to 14 inches of diameter and the LiPo battery between 2 and 4 cells. We rely on Multiplex‘ Roxxy Motor Finder (see www.multiplex-rc.de) and evaluate three of them.
| # | cells | airscrew | rpm | current | thrust |
|---|---|---|---|---|---|
| 1 | 3 | 10.5×6″ | 7’800 | 23 A | 1’070 g |
| 2 | 2 | 10.5×6″ | 5’900 | 13 A | 610 g |
| 3 | 2 | 14×8″ | 4’400 | 22 A | 875 g |
#1 is a hotliner setup. We are not sure whether the Taser’s delicate airframe would stand up to a thrust/weight ratio of almost 2:1. #2 is a sensible option with still enough thrust to climb vertically. But if we went for this one, our Roxxy components would be a little bit oversize. Our favourite is #3. Two LiPo cells rather than three means either more mAh or less weight and the slowly revolving airscrew with big diameter means less noise and vibrations.
4. Airscrew Assembly
The propeller blades need some rework. In addition to general deflashing, the edges of the blade roots are sanded to a 1.5 to 2mm radius to match the inner shape of the mount. The yellow marks pair the custom fit and balanced blades to their respective spinner locations. Just in case they have to be removed and reinstalled later.
Controller
The three motor connectors are soldered to the motor end of the controller and an XT60 connector to the battery end. Initially, in our case, the controller does not start the motor at settings below 50% throttle. We have to perfom the „learning procedure“ according to the manual to gain full response to the throttle stick.
On the motor side, we connect red to red, black to black and blue to yellow by intuition. Unfortunately, this causes the motor to rotate the wrong way round. Rather than switching the connected colours, the controller setting for parameter 2 „Direction of motor rotation“ is programmed to „Reverse“.
We decide not to switch on the motor brake at this stage but to do some test flights first.
Please note: The Roxxy 940-6 controller depicted here was replaced by the 930-4 type because is was oversized in terms of performance, dimensions and weight.
Test Run
This is the test setup
- fuselage taped to a heavy wooden beam with some rubber foam in between to avoid damage and for better vibration perception
- beam clamped to the table
- receiver test rig currently equipped with a Spektrum AR9020
- DX9 with an initial E-Taser model definition bound to the AR9020 on the test rig
- spare 2s LiPo 850 mAh battery
- multimeter for amperage
We keep an eye on the multimeter while throttle is opened slowly. The airscrew starts spinning very smothly. At 50% throttle the current is 5.15 amperes.
No vibrations. Unobtrusive sound. At full throttle, the reading is marginally below 20A. This is about what was to be expected according to Multiplex‘ calculated figures. Judged by the wind produced, we can hardly imagine ever using power settings above 80% in normal flight operation. The high loads imposed did not make the spinner creep on the driveshaft. Neither axial nor circular displacement can be measured. Test passed!
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